The present invention relates to a system for controlling the output of a Stirling engine.
The output of an external combustion engine known as a Stirling engine is determined by the pressure of a working gas in a working space. When it is desired to increase the engine output, for example, the pressure of the working gas in the working space is raised.
FIG. 1 of the accompanying drawings shows a typical example of an output control system for a Stirling engine as disclosed in Japanese Laid-Open Patent Publication No. 46-23534. The Stirling engine has working spaces 1 coupled to a compressor 3 through check valves 2 and a highest-cycle-pressure line 4 having a pressure reducing valve 5. The working spaces 1 are also coupled to the compressor 3 through check valves 6 and a lowest-cycle-pressure line 7 having a booster valve 8. A high-pressure tank 9 is connected to the booster valve 8 parallel to the compressor 3.
The booster valve 8 has its downstream end connected to a feedback piston cylinder 10 having a piston coupled through a piston rod to an accelerator lever 11 at an end thereof serving as a fulcrum 14. The accelerator lever 11 is positioned between valve rods 12, 13 of the valves 8, 5 for engagement therewith. The piston of the feedback piston cylinder 10 is movable dependent on the pressure in the lowest-cycle-pressure line 7 for displacing the position of the fulcrum 14 of the accelerator lever 11.
In operation, when the output of the Stirling engine is to be increased, the accelerator lever 11 is pushed to the left (as shown) to open the booster valve 8, thus allowing a working gas under pressure to be supplied from the compressor 3 or the tank 9 into the working spaces 1. For reducing the engine output, the accelerator lever 11 is pushed rightward to open the pressure reducing valve 5 for bleeding off some pressure into the compressor 3 to thereby reduce the pressure in the working spaces 1.
The prior output control system of the foregoing arrangement is disadvantageous for the following reasons. When the accelerator lever 11 is inadvertently pushed to the left while the engine is at rest, the booster valve 8 is opened and the working gas flows from the high-pressure tank 9 into the lowest-cycle-pressure line 7, thereby increasing the gas pressure in the working spaces 1. The gas pressure in the working spaces 1 is raised to a level higher than necessary to start the Stirling engine, with the result that difficulty will be experienced in getting the engine started, thus making it necessary to regulate the gas pressure in advance to avoid such difficulty. The Stirling engine or external combustion engine is shut down by stopping the supply of fuel to a combustion chamber, but it takes a long period of time for the engine to stop even after the fuel supply is cut off, the reason being that the gas pressure in the working spaces 1 is kept at an idling pressure. Another problem is that because a gas pressure setting required for starting the Stirling engine is higher than the idling pressure, it is required when starting the engine to raise the gas pressure from the idling pressure up to the pressure setting necessary for setting the engine into motion.